On Sunday, the government will send an emergency alert test to every mobile phone and tablet in the UK that is 4G and 5G compatible. At around 3pm on Sunday, the test will set off a loud siren-like alert that will last for roughly 10 seconds - even if your phone is on silent or do not disturb. If you have a hidden phone or tablet, the test this Sunday could reveal your device. To make sure your device is safe and stays silent, follow this guide to turn off the alerts: Steps to secure your iPhone